Guide
How to split expenses when people stay different numbers of days
A trip where everyone arrives and leaves together is the textbook case. In practice two people turn up on Wednesday, one leaves on Friday, and the question becomes: who pays what proportion of which cost?
Step 1: sort every expense
The sorting matters more than the formula. A nightly rental depends on presence; a one-off cleaning fee doesn't; an activity only involves the people who did it. Three families, three treatments.
Pro rata formula
share_i = amount × nights_i ÷ total person-nights
Total person-nights is simply the sum of everyone's nights: four people staying 5, 5, 3 and 2 nights make 15 person-nights.
Step 2: the full worked example
Four friends rent a house for a week. Marc and Julie stay 5 nights, Sonia 3, Karim 2. The rental is £840.00, shared groceries come to £216.40, and the end-of-stay clean is £90.00, billed once regardless of how many people slept there.
| Expense | Key | Marc / Julie | Sonia | Karim |
|---|---|---|---|---|
| Rental £840.00 | Nights (5/5/3/2) | £280.00 / £280.00 | £168.00 | £112.00 |
| Groceries £216.40 | Nights (5/5/3/2) | £72.14 / £72.13 | £43.28 | £28.85 |
| Cleaning £90.00 | Equal shares | £22.50 / £22.50 | £22.50 | £22.50 |
| Total owed | — | £374.64 / £374.63 | £233.78 | £163.35 |
Check: 374.64 + 374.63 + 233.78 + 163.35 = £1,146.40, exactly 840.00 + 216.40 + 90.00. On the groceries line, 216.40 × 5 / 15 = £72.133…, so the leftover penny goes to the first share: £72.14 for Marc, £72.13 for Julie.
Split four ways with no distinction, Karim would have paid £286.60 for two nights — nearly double his real share.
Variations and special cases
The house is booked before anyone's dates are fixed. Whoever books fronts the whole amount: that's an advance, not a split key. They end up in credit and get repaid at the end.
Someone stays an extra night alone. That night is one more person-night in their column, so pro rata assigns it to them automatically.
A late cancellation. If the night is charged anyway, it stays with the person concerned. If it isn't, it simply drops out of their night count.
Frequently asked questions
Should everything be pro rata by nights?
No. Pro rata suits costs that genuinely depend on presence: accommodation, groceries, shared meals. One-off costs committed for the whole group — end-of-stay cleaning, a non-refundable booking, a rental package — can be split equally.
How do I count someone who arrives mid-afternoon?
Count nights, not days: it's the one unit everybody reads the same way. Arriving at 10pm on Friday and leaving Sunday morning is two nights.
What if the house costs more because an extra bedroom was needed?
The extra cost belongs to the people who made it necessary. The cleanest fix is to record the extra room as its own expense, shared between the people sleeping in it.
Is pro rata always fairer than equal shares?
Not always. On a weekend where one person misses a single night, full pro rata causes more debate than it prevents. It really pays off once the gaps exceed a night or two over a week.
Editorial review — Written and reviewed by the Pivunio team. The methods described here are the ones the app itself uses, and they are covered by automated tests.